1. Field of Invention
This invention is related to capturing and printing still images from video data signals. In particular, this invention is directed to a system and method to improve the vertical alignment of images captured from video.
2. Description of Related Art
Video recorders, camcorders and VCRs, for example, provide a source of electronic video images. However, especially in consumer-quality video recorders, when still images are captured from the video data signal and printed, the quality of the captured and printed still images is often less than desired. Furthermore, these video recorders may inaccurately synchronize the video scanlines. This inaccurate synchronization causes the starting point of scanlines to drift horizontally from scanline to scanline, resulting in the common appearance of wiggles or jitters in the vertical lines of the image.
The NTSC television standard forms a full frame image from two separate fields captured {fraction (1/60)}th of a second apart. One field contributes the even scanlines of the image, while the other field provides the odd scanlines of the image. FIG. 1 shows the odd scanlines 10 and even scanlines 20 which form the full image frame. Furthermore, FIG. 1 illustrates a typical example of the horizontal drift that occurs from scanline to scanline within an even or odd field (intra-field drift) as well as the horizontal drift that occurs between the fields (inter-field drift).
The average scanline starting position between two scan lines of a field will generally be more correct then the starting position of any single scanline. Since the two fields are separated by time, the horizontal drift of the fields will be uncorrelated. Hence, the average scanline starting position between the two fields is likely to be more nearly correct than the average starting position of either field alone. By measuring the misalignment within and between the fields, detecting the wiggle or jitter is straightforward.
U.S. patent application Ser. No. 08/882,933, filed Jun. 26, 1997, U.S. Pat. No. 6,031,581 incorporated herein by reference in its entirety, discloses a system for removing color bleed in a television image adapted for digital printing. Specifically, the 933 application discloses a method for improving an image derived from a television or video tape signal source so that the image can be favorably printed. However, this requires the entire image frame to be stored in memory and several passes over the image to determine the correct alignment.
This invention provides systems and methods for removing horizontal drift in still images captured from video data signals.
This invention separately provides systems and methods for removing intra-field and inter-field drift from captured still images.
This invention separately provides systems and methods that determines an average start position of the scanlines within a field of a captured still image and/or between the two separate fields forming a captured still image.
These and other features and advantages of this invention are described in or are apparent from the following detailed description of the preferred embodiments.